1. Field of the Invention
The present invention relates to video systems, and, in particular, to systems for transcoding from HDTV video signals to NTSC video signals.
2. Description of the Related Art
Many common television (TV) systems operate in accordance with the NTSC system. For example, in a typical NTSC system as used in North America, images (also referred to as video pictures or video frames) are displayed at approximately 30 frames per second, and have a resolution of approximately 720 (h).times.480 (v) active pixels. Interlacing is typically used in such systems, in which 720.times.240 fields are received 59.94.apprxeq.60 times per second, to provide a frame rate of 29.97.apprxeq.30 frames/sec. Additionally, such systems broadcast and employ analog format, rather than digital format, signals.
High-definition TV (HDTV) systems broadcast digital video signals having different parameters than those of NTSC systems. For example, a typical HDTV video system transmits digital video data at 30 frames/sec (interlaced), having a resolution of 1920.times.1080 active pixels. Such systems typically have improved image quality, and are thus being employed more and more frequently. Some NTSC systems attempt to emulate certain aspects of HDTV systems, for example by using line doubling, field repeating, and interpolation techniques to simulate improved vertical resolution. Additionally, for image data recorded in the NTSC format, this data will need to be transformed, or "tanscoded," into the HDTV format, by such techniques.
As the HDTV standard grows in popularity, HDTV receiver systems capable of receiving and displaying HDTV signals will also become more common. However, many NTSC (non-HDTV) TV sets will remain in use even after HDTV signals are being broadcast. In some cases it may be prohibitively expensive, inefficient, or otherwise undesirable to dispose of the NTSC-compatible equipment, and replace it with HDTV-compatible receivers.